1. Field of the Invention
The present invention relates to an image pickup device with image blur correcting function, adapted for use in a video camera or the like.
2. Related Background Art
Image taking equipment such as video cameras or electronic camera in recent years have shown remarkable progress in compactization and in the multitude of functions.
On the other hand, the hand vibration has been a drawback inherent to such equipment. Particularly in a compact video camera, the vibration of the supporting hand or other support may cause a blur in the object image, resulting in an unpleasant image or a deterioration in the resolving power. This phenomenon is particularly conspicuous in the video camera provided with a lens of a high magnification, and the blur becomes larger and more noticeable at the telephoto side.
For this reason there have been proposed and commercialized various video cameras with a function for correcting the image blur resulting from the vibration of hand or of other causes (such function being hereinafter called blur correcting function). An example of such video cameras is a video camera 400 shown in FIG. 1, with electronic blur correcting function.
In such video camera 400, an image signal obtained from a solid-state image pickup element 410 under the control of a solid-state image pickup element drive control circuit 415 is supplied to an analog signal processing circuit 411, and, after predetermined signal processing therein, is digitized by an analog/digital (A/D) converting circuit 412 to obtain digital image data, which are stored in a field memory circuit 413 and are supplied to an image motion detecting circuit 416.
In case the video camera 400 is set, by an unrepresented switch, at a mode in which the blur correcting function is activated (hereinafter called blur correcting mode), the image motion detecting circuit 416 executes an image motion detecting process on the image data from the A/D converting circuit 412, and sends the result of detection to a field memory control circuit 417.
In response to the result of detection from the image motion detecting circuit 416, the field memory control circuit 417 controls the reading operation for the image data stored in the field memory circuit 413.
More specifically, the field memory control circuit 417 controls the read-out addresses of the field memory circuit 413 in such a manner that the image data of an area, smaller by a predetermined number of pixels, are read from the field memory circuit 413 to a digital signal processing circuit 414.
The read-out address of the field memory circuit 413 can be moved within an area of the difference between the image data stored in the field memory circuit 413 and those read therefrom.
Thus the field memory control circuit 417 can execute the correction of the image blur by moving the read-out address according to the result of detection from the image motion detection circuit 416, within such movable range of the read-out address.
The image data, read from the field memory circuit 413 under the control of the field memory control circuit 417, are supplied to the digital signal processing circuit 414, and are subjected therein to interpolation to the standard number of pixels matching the predetermined television system. Thus interpolated image data are supplied to and displayed on an unrepresented monitor.
On the other hand, there is known a video camera capable of correcting the image blur, utilizing an angular velocity sensor for detecting the vibration of the hand or of other causes and a variable angle prism (VAP) for correcting the image blur. In such a video camera, the object image is focused on the light-receiving face of a solid-state image pickup device through the VAP, and, in the blur correcting mode, a signal representing the vibration, obtained by a external sensor such as an angular velocity sensor, is subjected to a filtering process consisting of amplification after the elimination of the DC component thereof and cutting-off of the low-frequency components. Such filtering process provides the target value of the vertex angle of the VAP, according to which the angle of the VAP is varied to achieve optical correction of the image blur. However, if such video camera is stably placed for example on a tripod in the blur correcting mode, the blur of the object image resulting for example from the noises released from the angular velocity sensor may become significant. Therefore, in the video camera of the above-mentioned kind, it has been proposed, in case the video camera is identified to be in a stable state, to eliminate such noises in the output signal of the angular velocity sensor by limiting the frequency band of such output signal with a high-pass filter (HPF) of which cut-off frequency is shifted to a higher frequency. Such method prevents the blur in the object image, resulting from the noises released from the angular velocity sensor.
In the image pickup device such as the video camera 400, however, in case the device is in the blur correcting mode and is free from the vibration caused for example by hand, if the object itself to be captured by the solid-state image pickup element 410 vibrates, such vibration is detected by the image motion detecting circuit 416 and the blur correction is conducted by the result of such detection. In such case, there is encountered a defective situation where the background or the entire image area, which should appear standstill, is displayed in the vibrating state.
Also in the image pickup device such as the video camera with optical image blur correcting function utilizing the angular velocity sensor and the variable angle prism, in case such device is placed in a stable state and is free from the vibration caused for example by hand, the blur in the object image, resulting for example from the noises in the output signal of the angular velocity sensor, is prevented by limiting the frequency band of the output signal of the angular velocity sensor through a shift of the cut-off frequency of the high-pass filter to a higher frequency, but, if the video camera is equipped with the lens of an ultra high magnification, the complete prevention of the image blur cannot be achieved unless the cut-off frequency of the high-pass filter is shifted to a considerably higher frequency.
It is therefore conceivable, in such video camera, to shift the cut-off frequency of the high-pass filter to a considerably higher frequency if the device is in a stable state.
However, if a vibration is suddenly given after such frequency shift, it becomes necessary to execute the blur correction by returning the cut-off frequency of the high-pass filter to the ordinary state, but the returning of the cut-off frequency of the high-pass filter from such considerably higher shifted frequency to the ordinary cut-off frequency requires a certain time. For this reason, there is required an additional time before the effect of blur correction can be reached.
The present invention is proposed to resolve the drawbacks mentioned above, and a first object thereof is to provide an image pickup device capable of providing a satisfactory image, by executing exact blur correction of the image without erroneous operation according to the vibration state of the device.
A second object of the present invention is to provide an image pickup device capable of reducing the time required to obtain the effect of blur correction from the stable state.
The above-mentioned objects can be attained, according to a preferred embodiment of the present invention, by an image pickup device comprising image pickup means for taking the image of an object and thereby generating an image signal, memory means for storing the image signal obtained by the image pickup means, motion detecting means for detecting the motion of the image based on the image signal obtained by the image pickup means, readout control means for reading the image signal from the memory means by controlling the readout address according to the result of detection by the motion detecting means, and vibration detecting means for detecting the vibration of the image pickup means and controlling the function of the readout control means according to the result of such detection.
Also according to another preferred embodiment of the present invention, there is provided an image pickup device comprising image pickup means for taking the image of an object and thereby generating an image signal, vibration detecting means for detecting the vibration of the image pickup means, filter means with variable filter characteristics for passing the detection signal generated by the vibration detecting means, output control means for controlling the output of the filter means, control means for controlling the filter means and the output control means according to the detection signal, and optical vibration blur correcting means for optically correcting the blur in the image taken by the image pickup means, based on the output of the output control means.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following description which is to be taken in conjunction with the attached drawings.